U.S. Pat. No. 2,053,822 discloses a process for the manufacture of sulphonic acids, consisting in treating with sulphonating agents imidazole derivatives having the atom grouping
aromatic radical containing at the most 10 carbon atoms, R1 represents an alkyl radical containing at least 7 carbon atoms and R2 is a member selected from the group consisting of hydrogen and alkyl. None of the alkylating agents cited contains an aromatic group i.e. benzyl chloride is apparently not included. The aromatic nucleus R may comprise substituents, for example, sulpho groups. The 2-substituent may also be a methoxy-, ethoxy-, mercapto- or thioalkyl-group. U.S. Pat. No. 2,053,822 further discloses that new imidazoles are characterized by the atom grouping
wherein the radical R represents a sulphonated aromatic radical, wherein further the nature of the μ-substituent follows from the above enumerations, and wherein at least one of the two nitrogen atoms is linked with a radical R1. The examples disclose the reaction of dodecyl chloride, 2-chloroacetic acid dodecyl ester with μ-heptadecyl-benzimidazole followed by sulphonation.
Thermography is an image-forming process including a heating step and hence includes photothermography in which the image-forming process includes image-wise exposure and direct thermal processes in which the image-forming process includes an image-wise heating step. In direct thermal printing a visible image pattern is produced by image-wise heating of a recording material.
U.S. Pat. No. 3,704,130 discloses a method of preparing a photographic fine-grain silver halide emulsion, which comprises the step of precipitating the silver halide in an aqueous hydrophilic colloid medium in the presence of a compound corresponding to the following general formula: Z-A-X, wherein: each of Z and X (the same or different) stands for a heterocycle or a heterocycle with fused-on ring, said heterocycle comprising the moiety ═N—, and A stands for a chemical bond, alkylene, alkylene interrupted by oxygen or —N(R)— wherein R=hydrogen or alkyl comprising at most 4 C-atoms, arylene, alkenylene, —S-alkylene-S— or —S-alkylene, the alkylene groups of which can be interrupted by oxygen or —N(R)— wherein R has the same significance as above; said compound being present in an amount sufficient to restrain growth of silver halide grains. U.S. Pat. No. 3,704,130 discloses the following 2-alkylthio-benzimidazole-6-sulphonic acid compounds as Compound 7:
Compound 9:
and Compound 10:

U.S. Pat. No. 4,639,408 discloses a process for forming an image comprising a heating step wherein a silver halide light-sensitive photographic material is heated in the presence of a compound represented by formula (I)
wherein X represents an atomic group completing a carbocyclic aromatic ring or a heterocyclic aromatic ring; R1 is selected from selected from groups represented by formulae (A), (B), and (C):—SO2—R11  (A)—C(═O)—R11  (B)—P(═O)R11R12  (C)in which R11 and R12 each represents a substituted or unsubstituted alkyl group, a cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, an alkoxy or aryloxy group, an alkylthio or arylthio group, or a substituted or unsubstituted amino group, or R11 and R12 together form a 5-membered or 6-membered ring; R2 represents a group selected from the groups represented by R11; R1 and R2 together form a 5-membered or 6-membered ring; Q represents a hydrogen atom, an alkyl group, or an aryl group; TIME represents a timing group; PUG represents a photographically useful group; and n represents 0 or an integer, wherein the photographic material contains a base or a base precursor. U.S. Pat. No. 4,639,408 discloses the following 2-alkylthio-benzimidazole-6-sulphonic acid compounds as Compound (8):
Compound (14):
Compound (24):
Compound 25:
and Compound 29:

U.S. Pat. No. 3,901,769 discloses in an electrical recording member provided with a recording layer containing an image-forming agent, an electrically-conductive agent and a binder therefor, the improvement comprising said electrically-conductive agent comprising at least a porous compound containing therein a polar substance, wherein an image is formed on said layer by the application thereto of electrical current and discloses that the polar substance can be oleyl (CH3(CH2)7CH═CH(CH2)8—) benzimidazole sulphonic acid.
Surfactants with excellent latex-stabilizing properties, which enhance the adhesion of hydrophilic layers to hydrophobic supports, such as polyethylene terephthalate and hydrophobic thermosensitive elements of substantially light-insensitive thermographic recording materials, which are photographically inactive, which do not contain photographically inactive impurities and which is compatible with image-wise heating with a thermal head when incorporated into the outermost layer of substantially light-insensitive thermographic recording materials.
ULTRAVON™ W, an anionic alkyl, benzyl-benzimidazole-sulfonic acid surfactant produced by Ciba, fulfils these requirements, except that being a mixture of at least 25 components it has variable properties and also often contains photographically active impurities, which have to be removed or rendered non-photographically active prior to use. Furthermore, it is no longer available.